1. Field of the Invention
The invention relates to the field of lighter-than-air vehicles and, in particular, to an improved ballonets and a system for pressurizing same.
2. Description of Related Art
There are three general types of non-rigid vehicles: those comprising a single gas filled bag; several gas bags joined together in series; and, of course, those having a multiple number of gas bags within a non-rigid envelope. One of the major problems with non-rigid lighter-than-air vehicles is keeping the bag from bursting as the ambient pressure decreases with altitude or from collapsing when descending from altitude. The main method of preventing such events is to incorporate ballonets in the vehicle, which are inflatable gas bags within the Helium bag. The vehicle is designed to fly with partially inflated ballonets that can be inflated with air, causing the Helium volume to contract or, deflated, causing the Helium volume to expand. Thus, at altitude, the ballonets may be almost collapsed, providing the necessary "room" for the Helium to expand as ambient air pressure has decreased. As the vehicle descends into denser atmosphere, the ballonets are inflated to insure that the Helium gas bag does not collapse or even locally sag. Additionally, ballonents can play a roll in altitude control. An example of ballonets installed on a lighter-than-air vehicle can be found in U.S. Pat. No. 5,143,322, "Ground Handling, Altitude Control And Longitudinal Stability Of Airships" by E. W. Mason.
Prior art methods of pressurizing and filling the ballonets typically involved the use of ram air scoops. Examples of this type system can be found in U.S. Pat. Nos. 1,475,210, "Airship" by R. H. Upson and 2,331,404, "Airship" by H. R. Liebert. In the Liebert design, the ram air scoops are located behind the propellers and thus less dependent upon the speed of the airship. However, if the ship were at very low speeds filling, of course, would be proportionally slower. This would be true even with the Liebert design, because the speed of the airship is proportional to the rotational speed of the propeller.
In U.S. Pat. Nos. 1,580,004, "Airship" by A. Bradford and 1,797,502, "Airship by C. S. Hall separate pumps are used for pressurizing the ballonets. Additionally, the Hall design provide heaters to heat the pressurized air. Since the ballonet is located in the middle of the main Helium filled gas bag, heating of the Helium could also be accomplished. The problem with these designs is that the ballonets are located centrally and fill valves and lines are, necessarily, co-located. Thus they are difficult to reach for maintenance and repair or removal. Additionally, the need for such fill valves and lines add weight.
Co-pending U.S. patent application Ser. No. 08/155,363 "Ballonet System For A Lighter-Than-Air Vehicle" by J. B. Kalisz, et. al. (common assignee) also discloses a ballonet system for a lighter-than-air-vehicle. In detail, the ballonet system includes a plurality of ballonets located within the gas bag positioned along the longitudinal axis and on each side of the vertical axis of the vehicle. Each of the ballonets include a flexible sheet joined at its periphery thereof to a portion of the wall of the gas bag. A ballonet pressurization system is coupled to each ballonet for pressurizing them with air that includes the portion of the wall of the gas bag forming the ballonet having a plurality of holes therethrough. A manifold having an inlet port is joined to the wall covering the holes therein and is adapted to diffuse the pressurized air entering therein. Also included is at least one fan having an inlet port coupled to ambient atmosphere and an outlet port coupled to the inlet port of the manifold for providing pressurized air to the interior thereof. A check valve located in the outlet port of the fan is provided for preventing air from flowing from the interior of the manifold out the inlet port of the fan. A ballonet venting system is included for venting the interior of the ballonet to ambient atmosphere. However, it does not provide for very rapid deflation of the ballonet.
Thus, it is a primary object of the invention to provide a ballonet system for a lighter-than-air vehicle.
It is another primary object of the invention to provide a ballonet system for a lighter-than-air-vehicle that is independent from other systems of the vehicle.
It is a further object of the invention to provide a ballonet system for a lighter-than-air vehicle that allows the volume of air in each ballonet to be individually varied.
A still further object of the invention is to provide a ballonet system for a lighter-than-air vehicle that provides rapid inflation and deflation of the individual ballonets.